Creating a Custom Comparator 1

[brinker]

Hi,

I have been trying to figure out how to create a custom comparator that I can use to handle a list of items of a user defined data type. For instance:

class mytype
{
int a;
String b;
String c;
URL d;
}

If I want a comparator that can order these items by int a, how could I construct it...and use it. I know that there must be a way as Java has a Comparator interface.

thanks

Brinker

 

[Tarwn]

You could write a quick compare method inside your mytype class like so:

public int compare(int comparee){
   if(comparee > a){
      return 1;
   }
   if(comparee = a){
      return 0;
   }
   if(comparee < a){
      return -1;
   }
}

Just a thought
-Tarwn --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---

http://www.tuxedo.org/~esr/faqs/smart-questions.html

 

[MarsChelios]

RTFAPI

http://java.sun.com/j2se/1.4.1/docs/api/java/util/Comparator.html

MarsChelios

 

[toolkit]

when comparing int members your comparator implementation needs to have:

public int compare(Object o1, Object o2) {
  mytype mt1 = (mytype)o1;
  mytype mt2 = (mytype)o2;
  return (mt1.a - mt2.a);
}

Its as simple as that for int members.

For String members, you should use something like:

public int compare(Object o1, Object o2) {
  mytype mt1 = (mytype)o1;
  mytype mt2 = (mytype)o2;
  return (mt1.b.compareTo(mt2.b));
}

You can even make your comparator sort on an int, and then a string using:

public int compare(Object o1, Object o2) {
  mytype mt1 = (mytype)o1;
  mytype mt2 = (mytype)o2;
  int ret = mt1.a - mt2.a;
  if(ret != 0)
    return ret;
  else
    return (mt1.b.compareTo(mt2.b));
}

etc.. Hope this helps

 

[brinker]

Yes, this helps quite a bit.

 

[brinker]

Any Tips on how to make a comparator to compare float numbers? I believe that maybe just multiplying the numbers by 10E5 might be the way, but it is not too efficient.